linux-kernel - [PATCH] netlink: drop (int) cast on length arg in NLMSG

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Message-Id: <1425534428-24182-1-git-send-email-vapier@gentoo.org>
Date:	Thu,  5 Mar 2015 00:47:08 -0500
From:	Mike Frysinger <vapier@...too.org>
To:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] netlink: drop (int) cast on length arg in NLMSG_OK

The NLMSG_OK macro compares three things:
 - the len arg from the user
 - a size_t: sizeof(struct nlmsghdr)
 - an int: sizeof(struct nlmsghdr) casted
 - an u32: the nlmsghdr->nlmsg_len member

When building with -Wsign-compare, this macro triggers a signed compare
warning.  This is because it compares len to an int, and then compares
it to a u32.  If len is signed, we get a warning due to the last test.
If len is unsigned, we get a warning due to the first test.  Like in
strace:
socketutils.c:145:8: warning: comparison between signed and unsigned
                              integer expressions [-Wsign-compare]

Lets drop the int cast on the first sizeof.  This way, once the user
casts len to an unsigned value, everything shakes out correctly.

Signed-off-by: Mike Frysinger <vapier@...too.org>
---
 include/uapi/linux/netlink.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index 1a85940..3eb4e24 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -84,7 +84,7 @@ struct nlmsghdr {
 #define NLMSG_DATA(nlh)  ((void*)(((char*)nlh) + NLMSG_LENGTH(0)))
 #define NLMSG_NEXT(nlh,len)	 ((len) -= NLMSG_ALIGN((nlh)->nlmsg_len), \
 				  (struct nlmsghdr*)(((char*)(nlh)) + NLMSG_ALIGN((nlh)->nlmsg_len)))
-#define NLMSG_OK(nlh,len) ((len) >= (int)sizeof(struct nlmsghdr) && \
+#define NLMSG_OK(nlh,len) ((len) >= sizeof(struct nlmsghdr) && \
 			   (nlh)->nlmsg_len >= sizeof(struct nlmsghdr) && \
 			   (nlh)->nlmsg_len <= (len))
 #define NLMSG_PAYLOAD(nlh,len) ((nlh)->nlmsg_len - NLMSG_SPACE((len)))
-- 
2.3.1

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